Friday, June 26, 2015

Is dry the new normal?

We've been very dry here across South Florida (see previous post for detailed numbers) and if long range outlooks are correct, brown may be the new green. We typically get between 35-45" of rain during the wet season which is about 70% of our annual rain budget. Rain now, we basically have a few drops in the bucket.

Lets take a quick look at the Rainy Season Outlook offered back in mid May.

The forecast:

  • The rainy season officially began May 10th (avg start is around May 20th)
  • Even with the early start, the NWS forecast was for a “Near to Slightly Below Normal” Rainy Season.
  • May and June were supposed to be the wettest with above average rain with drying conditions starting in July and running through mid October.

Rain so far:

  • May rainfall in Miami was only 2.39" with the average being 5.34"
  • Ft. Lauderdale had 1.97" with the norm being 4.65"
  • Key West 1.12" in May, with typical being 3.00"
  • Add to that the June numbers (previous post) and we are way below what's normal. Many areas across South Florida are in drought status.

So if, May and June were to be the wettest of the rainy season, and the upcoming months are forecast to be drier... its going to be very thirsty and hot through the rest of the season. Expect those green lawns to turn a little brown.

How did NWS arrive at the rainy season outlook?:
The outlook of near to slightly below normal precipitation is based on a combination of several factors:

  • Historical data (comparing past summers with similar atmospheric conditions to what is expected this summer)
  • Long-range models
  • The official NOAA Climate Prediction Center outlooks
  • And observed conditions over the past 10-20 years

Back then NWS said the main factor influencing their outlook was the phenomenon known as "El Niño". This is a warming of the equatorial waters of the Pacific which impact both marine and atmospheric wind patterns. Its akin to shaking a snow globe, it messes with the atmosphere causing droughts in typically wet areas and the opposite in the soggy regions of the earth.

They did say: 
Its important to note that not every El Niño event has the same effects on Florida’s weather.

The rainy season usually has three phases:
- Late May through early July (“stormiest” part of the season- and so far its been very dry).
- Early July through mid-August (hotter with dry periods-and its been sizzling so far).
- Late August through mid-October (higher rainfall variability due to potential tropical systems and early-fall cold fronts).

Short term forecast:
We are hoping for some rain this Friday and Saturday as high pressure moves away. If not, next week the high pressure dome that has kept most of the rain away, will return with a vengeance. We'll be back to mostly dry and possibly hotter. Plus, African dust is expected to move in drying us out even more and bringing us hazy skies.

Long range: 
I never thought I would say this, but we need a tropical wave to bring us much needed rain. Keep your fingers crossed.

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